Unsaturated monomers, particular olefin monomers, are polymerized in a variety of polymerization processes using a wide variety of catalysts and catalyst systems. One of the most common polymerization process used in the production of olefin based polymers such as polyethylene, polypropylene, polybutene, etc, is a solution based process. In such a process the formed polymer is dissolved in the polymerization medium. Often, the catalyst and monomer are also dissolved in the polymerization medium, but that is not a requirement of a “solution” process. In typical solution processes, the polymerization temperature may be at, above or below the melting point of the dry polymer. For example, in typical solution phase polyethylene processes, polymerization takes place in a hydrocarbon solvent at temperatures above the melting point of the polymer and the polymer is typically recovered by vaporization of the solvent and any unreacted monomer. In some cases solvents are used as the polymerization medium while in others, the monomer to be polymerized also acts as the solvent (e.g. a bulk process).
In each of these systems, there remain factors that influence not only the rate and volume at which the polymerization can run, but can also influence the properties of polymer produced. In a solution process, the polymer formed is dissolved in the polymerization medium. The higher the concentration of the polymer, the higher the viscosity of the polymerization reaction mixture containing polymer, monomers and solvent. High viscosity in the polymerization reactor associated with solution process is a limiting step for process efficiency and polymer production. High viscosity can also lead to the difficulty for efficient mixing in the reactor to maintain a homogeneous system and avoid product property drift (heterogeneity), reactor safety, process control problems. This is especially true for processes of polymerization with polymers having molecular weights higher than the entanglement molecular weights. Higher operating temperature reduces the viscosity, however the molecular weight of the polymer tends to decrease with reaction temperature. Thus production of higher molecular weight polymers in solution processes is generally limited by the viscosity of the polymerization medium. This problem exists even with the advent of new catalyst systems. In some situations, metallocene catalysts allow polymerizations to be performed at a high temperatures, such that a higher polymer concentration in the reactor effluent is obtained (as compared to that of a conventional solution process) with reduced operation difficulties.
Polymer solutions can undergo phase separation at the lower critical solution temperature. The phase separation is encouraged by higher temperature and/or lower pressure. Appropriate selection of polymerization solvent, monomer conversion, especially of the volatile monomers, temperatures, and pressures is required to avoid phase separation. Solvents such as hexane may require an elevated operating pressure of above 50 bar (5000 kPa) to avoid unwanted phase separation. In solution plants, solvent selection and operating conditions must be designed for a particular operating windows for the desired polymerization process. This operating window might not be permitted by or optimized for a given polymer type and catalyst.
Polymers with low crystallinity or amorphous character as well as those with higher crystallinities are currently produced in slurry and or suspension processes using hydrocarbon solvents as diluents. The suspension process can advantageously handle polymer concentrations in the reactor effluent up to 25-30 wt %, as compared to 7-18 wt % in the solution process which are limited by solution viscosity at a high level of solids content. These higher concentrations are attributable to the characteristics of decreasing polymer-polymer entanglements in the suspension process by forcing the entangled polymer into the dispersed and or suspended phase thereby decreasing the concentration of entangled polymer in the bulk reactor solution phase. The recovery of polymer is also simpler in the slurry process. However, it is necessary that the solid particles in the slurry process do not agglomerate to one another or adhere to the surfaces of the reactor wall and the transport lines. Extremely low operating temperatures are adopted to reduce the soluble fraction of polymer in the solvent. Mitigation of polymer fouling is a challenging task.
Many polymers are insoluble in the reaction mixture from which they are formed. Upon significant polymerization, polymer chains reach a crystallizable length and polymer nucleation and crystallization begin. The crystallization of polymers leads to polymer-solvent phase separation. On the other hand, polymer-solvent phase separation can be also induced through change of solvency of the reaction medium with respect to the polymer produced. The instant invention provides a process that with proper selection of a fluorinated hydrocarbon or a mixture of fluorinated hydrocarbons and hydrocarbon solvents, can be operated in a suspension mode instead of solution. There is a need for polymerization processes which efficiently produce polymer, particularly of higher molecular weight, with reduced operation difficulties and/or reduced reactor fouling.
U.S. Pat. No. 3,470,143 discloses a process to produce a boiling-xylene soluble polymer in a slurry using certain fluorinated organic carbon compounds.
U.S. Pat. No. 5,990,251 discloses a gas phase process using a Ziegler-Natta catalyst system modified with a halogenated hydrocarbon, such as chloroform.
EP 0 459 320 A2 discloses polymerization in polar aprotic solvents, such as halogenated hydrocarbons.
U.S. Pat. No. 5,780,565 discloses dispersion polymerizations of polar monomers under super-atmospheric conditions such that the fluid is a liquid or supercritical fluid, the fluid being carbon dioxide, a hydrofluorocarbon, a perfluorocarbon or a mixture thereof.
U.S. Pat. No. 5,624,878 discloses the polymerization using “constrained geometry metal complexes” of titanium and zirconium.
U.S. Pat. Nos. 2,534,698, 2,644,809 and 2,548,415 disclose preparation of butyl rubber type elastomers in fluorinated solvents.
U.S. Pat. No. 6,534,613 discloses use of hydrofluorocarbons as catalyst modifiers.
U.S. Pat. No. 4,950,724 disclose the polymerization of vinyl aromatic monomers in suspension polymerization using fluorinated aliphatic organic compounds.
WO 02/34794 discloses free radical polymerizations in certain hydrofluorocarbons.
WO 02/04120 discloses a fluorous bi-phasic systems.
WO 02/059161 discloses polymerization of isobutylene using fluorinated co-initiators.
EP 1 323 746 discloses a method of supporting a catalyst using soluble and insoluble liquids, such as hydrocarbon/halocarbon mixtures. Example 1 of EP 1 323 746 shows loading of biscyclopentadienyl catalyst onto a silica support in perfluorooctane and thereafter the prepolymerization of ethylene at room temperature.
U.S. Pat. No. 3,056,771 discloses polymerization of ethylene using TiCl4/(Et3Al in a mixture of heptane and perfluoromethylcyclohexane, presumably at room temperature. Additional references of interest include: Designing Solvent Solutions, Chemical and Engineering News, Oct. 13, 2003 (www.CEN-online.org); Polymer Synthesis Using Hydrofluorocarbon Solvents., Wood, Colin, et al. Macromolecules, Vol. 35, Number 18, pages 6743-6746, 2002; Perfluorinated Polyethers for the Immobilisation of Homogeneous Nickel Catalysts, Keim, W. et al., Journal of Molecular Catalysis A: Chemical 139 (1999) 171-175; RU2195465; US20020086908 A1; WO200251875 A1; US2002/0032291 A1; U.S. Pat. Nos. 3,397,166; 3,440,219; 6,111,062;5,789,504; 5,703,194; 5,663,251; 5,608,002; 5,494,984; 5,310,870; 5,182,342; 2,603,626; 2,494,585; 2,474,571; WO 02/051875 A1; U.S. Pat. Nos. 6,133,389; 6,096,840; 6,107,423; 6,037,483; 5,981,673; 5,939,502; 5,939,501; 5,674,957; 5,872,198; 5,959,050; 5,821,311; 5,807,977; 5,688,838; 5,668,251; 5,668,250; 5,665,838; 5,663,255; 5,552,500; 5,478,905;5,459,212; 5,281,680; 5,135,998; 5,105,047; 5,032,656;4,166,165; 4,123,602; 4,100,225; 4,042,634; US 2002/0132910 A1; US 2002/0151664 A1; US 2002/0183457 A1; US 2002/0183471 A1; US 2003/0023013 A1; US 2001/0012880 A1; US 2001/0018144 A1; US 2002/0002219 A1; US 2002/0028884 A1; US 2002/0052454 A1; US 2002/0055580 A1; US 2002/0055581; US 2002/0055599 A1, US 2002/0065383; US 2002/0086908 A1; US 2002/0128411 A1; U.S. Pat. Nos. 3,269,972, 3,331,822;3,493,530; 3,528,954; 3,590,025; 3,616,371; 3,642,742;3,787,379; 3,919,183; 3,996,281; 4,194,073; 4,338,237; 4,381,387; 4,424,324; 4,435,553; 4,452,960; 4,499,249;4,508,881; 4,535,136; 4,588,796; 4,626,608; 4,736,004;4,900,777; 4,946,936; 4,948,844; WO00/50209; WO/96/24625; WO 94/17109; WO 0149760 A1; WO 01/49758 A1; WO 01/49757; WO 00/53682; WO 00/47641; U.S. Pat. Nos. 6,486,280 B1; 6,469,185 B1 ; 6,469,116 B2;6,455,650 B1; 6,448,368 B1; 6,423,798 B2; EP 0 076 511 B1; EP 0 271 243 B1; U.S. Pat. Nos. 6,417,314 B1; 6,399,729 B1; 6,380,351 B1; 6,372,838 B1; 6,346,587 B1; 6,337,373 B1; 6,335,408 B1; 6,306,989 B1; 6,228,963 B1; 6,225,367 B1; JP 7033821 B published Apr. 12, 1995; JP 11349606 A published Dec. 21, 1999; and JP 61007307 published Jan. 14, 1986.